PowerPoint Presentation DNA A New Forensic Science Tool DNA A New Forensic Science Tool Chapter 13 What is DNA?What is DNA? • Deoxyribonucleic Acid • Double Helix • Basis of all inheritance • Used as[.]
DNA: A New Forensic Science Tool Chapter 13 What is DNA? • Deoxyribonucleic Acid • Double Helix • Basis of all inheritance • Used as a diagnostic tool for genetic disorders • DNA “fingerprinting” “profiling” or “typing” • Link evidence to person with relative certainty What is DNA? • Individual unit called NUCLEOTIDE • Individual unit called NUCLEOTIDE – Sugar – Phosphate – Base • DNA bases are – Adenine – Cytosine – Guanine – Thymine –These four letters make up the DNA alphabet that is the language of the cell What is DNA? • Double Helix • Double Helix • • A always pairs with T C always pairs with G What is DNA? • DNA is the ‘recipe’ for who we are: – HEIGHT – EYE COLOR – FINGERS & TOES – PROTEINS – ORGANS – LIVING FUNCTIONS • Found in virtually all 60 trillion cells in the human body • DNA in each cell is identical – Similar to ‘fingerprints’ DNA in the Cell cell nucleus chromosome Double stranded DNA molecule Target Region for PCR Individual nucleotides HISTORY OF DNA • 1954 - Watson & Crick describe the structure (Nobel Prize) • 1985 - Alec Jeffreys discovers multilocus VNTR probes • 1985 - Mullis develops protocol for polymerase chain reaction (PCR) (Nobel Prize) • 1988 - FBI starts DNA casework • 1991 - first STR paper • 1998 - FBI launches CODIS database What type of cases are investigated? • Forensic cases matching suspect with • • • • evidence Paternity testing identifying father Historical investigations Missing persons investigations Mass disasters putting pieces back together • Military DNA “dog tag” • Convicted felon DNA databases What type of samples are submitted? • Blood • Semen • Saliva • Urine • Hair • Teeth • Bone Buccal (CHEEK) swabs primarily • Tissue used as DNA knowns today Probative Items To Look For • Glasses • Hat • Belt • Gum • Beer / coke can • Toothpick • Phone • Cigarette PCR Copies DNA Exponentially through Multiple Thermal Cycles Original DNA target region Thermal cycle In In32 32cycles cyclesat at100% 100%efficiency, efficiency,1.07 1.07billion billion copies copiesof oftargeted targetedDNA DNAregion regionare arecreated created PCR • THERMAL CYCLER is used to amplify • CYCLES TEMPERATURES to – Separate strands – Anneal primers – Extend strand copy – Repeat PCR ADVANTAGES • Small sample size required • Short turn around time • Automation possible • Fluorescent tags instead of radioactivity • Precise allele size Short Tandem Repeats (STRs) AATG repeats repeats the repeat region is variable between samples while the flanking regions where PCR primers bind are constant Homozygote = both alleles are the same length Heterozygote = alleles differ and can be resolved from one another